Microbial Biosensors
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Analytica Chimica Acta 568 (2006) 200–210 Review Microbial biosensors Yu Lei a,∗, Wilfred Chen b, Ashok Mulchandani b,∗ a Division of Chemical and Biomolecular Engineering and Centre of Biotechnology, Nanyang Technological University, Singapore 637722, Singapore b Department of Chemical and Environmental Engineering, University of California, Riverside, CA 92521, USA Received 29 August 2005; received in revised form 17 November 2005; accepted 21 November 2005 Available online 18 January 2006 Abstract A microbial biosensor is an analytical device that couples microorganisms with a transducer to enable rapid, accurate and sensitive detection of target analytes in fields as diverse as medicine, environmental monitoring, defense, food processing and safety. The earlier microbial biosensors used the respiratory and metabolic functions of the microorganisms to detect a substance that is either a substrate or an inhibitor of these processes. Recently, genetically engineered microorganisms based on fusing of the lux, gfp or lacZ gene reporters to an inducible gene promoter have been widely applied to assay toxicity and bioavailability. This paper reviews the recent trends in the development and application of microbial biosensors. Current advances and prospective future direction in developing microbial biosensor have also been discussed. © 2005 Published by Elsevier B.V. Keywords: Microbial biosensors; Amperometric; Potentiometric; Optical; Luminescence; Fluorescence Contents 1. Introduction ............................................................................................................ 201 2. Advantages of using microorganisms as biosensing elements ................................................................ 201 3. Immobilization of microorganisms ........................................................................................ 201 3.1. Chemical methods ................................................................................................ 201 3.2. Physical methods ................................................................................................. 201 4. Electrochemical microbial biosensor ...................................................................................... 202 4.1. Amperometric microbial biosensor ................................................................................. 202 4.2. Potentiometric microbial biosensor ................................................................................. 204 4.3. Conductimetric biosensor .......................................................................................... 205 4.4. Microbial fuel cell type biosensor................................................................................... 205 5. Optical microbial biosensor .............................................................................................. 205 5.1. Bioluminescence biosensor ........................................................................................ 205 5.2. Fluorescence biosensor ............................................................................................ 207 5.2.1. Green fluorescence protein-based biosensor.................................................................. 207 5.2.2. O2-sensitive fluorescent material-based biosensor ............................................................ 207 5.3. Colorimetric biosensor ............................................................................................ 207 6. Other types of microbial biosensors ....................................................................................... 208 6.1. Sensors based on baroxymeter for the detection of pressure change .................................................... 208 6.2. Sensors based on infrared analyzer for the detection of the microbial respiration product CO2 ............................. 208 7. Future trends ........................................................................................................... 208 Acknowledgements ..................................................................................................... 208 References ............................................................................................................. 208 ∗ Corresponding authors. Tel.: +65 67906712; fax: +65 67947553. E-mail addresses: [email protected] (Y. Lei), [email protected] (A. Mulchandani). 0003-2670/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.aca.2005.11.065 Y. Lei et al. / Analytica Chimica Acta 568 (2006) 200–210 201 1. Introduction ers with a close proximity. Since microbial biosensor response, operational stability and long-term use are, to some extent, a A biosensor is an analytical device that combines a bio- function of the immobilization strategy used, immobilization logical sensing element with a transducer to produce a signal technology plays a very important role and the choice of immo- proportional to the analyte concentration [1–18]. This signal bilization technique is critical. Microorganisms can be immobi- can result from a change in protons concentration, release lized on transducer or support matrices by chemical or physical or uptake of gases, light emission, absorption and so forth, methods [1–6]. brought about by the metabolism of the target compound by the biological recognition element. The transducer converts this 3.1. Chemical methods biological signal into a measurable response such as current, potential or absorption of light through electrochemical or Chemical methods of microbe immobilization include cova- optical means, which can be further amplified, processed and lent binding and cross-linking [1–6,24]. Covalent binding meth- stored for later analysis [1–3]. ods rely on the formation of a stable covalent bond between Biomolecules such as enzymes, antibodies, receptors, functional groups of the microorganisms’ cell wall components organelles and microorganisms as well as animal and plant such as amine, carboxylic or sulphydryl and the transducer such cells or tissues have been used as biological sensing elements. as amine, carboxylic, epoxy or tosyl. To achieve this goal, whole Among these, microorganisms offer advantages of ability to cells are exposed to harmful chemicals and harsh reaction con- detect a wide range of chemical substances, amenability to dition, which may damage the cell membrane and decrease the genetic modification, and broad operating pH and tempera- biological activity. How to overcome this drawback is still a ture range, making them ideal as biological sensing materials challenge for immobilization through covalent binding. To our [1–18]. Microorganisms have been integrated with a variety of knowledge, this method has therefore not been successful for transducers such as amperometric, potentiometric, calorimetric, immobilization of viable microbial cells [1–17,24]. conductimetric, colorimetric, luminescence and fluorescence to Cross-linking involves bridging between functional groups construct biosensor devices [1–8]. Several reviews papers and on the outer membrane of the cells by multifunctional reagents book chapters addressing microbial biosensor development have such as glutaraldehyde and cyanuric chloride, to form a net- been published [1–20]. The intent of this review is to highlight work. Because of the speed and simplicity, the method has found the advances in the rapidly developing area of microbial biosen- wide acceptance for immobilization of microorganisms. The sors with particular emphasis to the developments since 2000. cells may be cross-linked directly onto the transducer surface or on a removable support membrane, which can then be placed 2. Advantages of using microorganisms as biosensing on the transducer [1–17,24]. The ability to replace the membrane elements with the immobilized cells is an advantage of the latter approach. While cross-linking has advantages over covalent binding, the Enzymes are the most widely used biological sensing ele- cell viability and/or the cell membrane biomolecules can be ment in the fabrication of biosensors [1–4]. Although puri- affected by the cross-linking agents. Thus cross-linking is suit- fied enzymes have very high specificity for their substrates able in constructing microbial biosensors where cell viability is or inhibitors, their application in biosensors construction may not important and only the intracellular enzymes are involved in be limited by the tedious, time-consuming and costly enzyme the detection [8]. purification, requirement of multiple enzymes to generate the measurable product or need of cofactor/coenzyme. Microor- 3.2. Physical methods ganisms provide an ideal alternative to these bottle-necks [15]. The many enzymes and co-factors that co-exist in the Adsorption and entrapment are the two widely used physical cells give the cells the ability to consume and hence detect methods for microbial immobilization. Because these meth- large number of chemicals; however, this can compromise the ods do not involve covalent bond formation with microbes and selectivity. They can be easily manipulated and adapted to provide relatively small perturbation of microorganism native consume and degrade new substrate under certain cultivating structure and function, these methods are preferred when viable condition [21–23]. Additionally, the progress in molecular biol- cells are required [8,14–17,24]. ogy/recombinant DNA technologies has opened endless possi- Physical adsorption is the simplest method for microbe bilities of tailoring the microorganisms